A major portion of small commercial-property deals in the United States have fallen through because of stricter lending standards, according to a survey by the National Association of Realtors.

While the commercial real estate market showed signs of recovery in 2011, credit tightened in the past year for small businesses, the group said on Thursday. Two of every three agents who have helped clients buy properties for less than $2 million said that purchases were scuttled because of a lack of capital, according to the survey.

Small-business transactions rely heavily on regional and local banks, and 30 percent of the purchases of properties like apartments, offices and warehouses were made with cash, according to the survey.

"This is very much a tale of two markets," said Lawrence Yun, the group’s chief economist. "There have been notable improvements in capital for large commercial transactions valued at $2.5 million or higher, but there remain significant challenges for small businesses."

More than half the respondents said lending was just as stringent as a year ago, 23 percent said it was tighter, and 20 percent said it was easier to obtain financing.

The survey was conducted last month. A random sample of 32,459 Realtors with an interest in commercial real estate were asked to complete the online questionnaire, and 474 responded.